What do you do when your e-mail account gets hacked?

As far as I can tell, my contacts were erased and replaced with five addresses unknown to me.
Beyond changing my password, what else should I do? Are the people who were in my address book susceptible to any viruses or anything?

Do not keep the same email account. Delete it and start over. Since they already got your contacts, there's no reason to try and salvage it. Also, if you aren't already, run a virus scan and then something for spyware and adware. More than likely they were just trying to use your email, but it's possible they got into your system somehow too. I would hate to think there is some sort of keylogger or something on there.